Food losses due to crop infections from pathogens such as bacteria, viruses and fungi are persistent issues in agriculture for centuries across the globe. In order to minimize the disease induced damage in crops during growth, harvest and postharvest processing, as well as to maximize productivity and ensure agricultural sustainability, advanced disease detection and prevention in crops are imperative. This paper reviews the direct and indirect disease identification methods currently used in agriculture. Laboratory-based techniques such as polymerase chain reaction (PCR), immunofluorescence (IF), fluorescence in-situ hybridization (FISH), enzyme-linked immunosorbent assay (ELISA), flow cytometry (FCM) and gas chromatography-mass spectrometry (GC-MS) are some of the direct detection methods. Indirect methods include thermography, fluorescence imaging and hyperspectral techniques. Finally, the review also provides a comprehensive overview of biosensors based on highly selective bio-recognition elements such as enzyme, antibody, DNA/RNA and bacteriophage as a new tool for the early identification of crop diseases.

Spinach thylakoids were immobilized onto multiwalled carbon nanotubes using a molecular tethering chemistry. The resulting thylakoid-carbon nanotube composites showed high photo-electrochemical activity under illumination. Multiple membrane proteins have been observed to participate in direct electron transfer with the electrode, resulting in the generation of photocurrents, the first of its kind reported for natural photosynthetic systems. Upon inclusion of a mediator, the photo-activity was enhanced. The major contributor to the photocurrent was the light-induced water oxidation reaction at the photosystem II complex. The thylakoid-MWNT composite electrode yielded a maximum current density of 68 mA cm À2 and a steady state current density of 38 mA cm À2 , which are two orders of magnitude larger than previously reported for similar systems. The high electrochemical activity of the thylakoid-MWNT composites has significant implications for both photosynthetic energy conversion and photofuel production applications. A fuel cell type photosynthetic electrochemical cell developed using a thylakoid-MWNT composite anode and laccase cathode produced a maximum power density of 5.3 mW cm À2 , comparable to that of enzymatic fuel cells. The carbon based nanostructured electrode has the potential to serve as an excellent immobilization support for photosynthetic electrochemistry based on the molecular tethering approach as demonstrated in this work. Broader contextThe article reports a photosynthetic electrochemical cell composed of a thylakoid-based photo-anode and laccase based enzymatic cathode. The cell generates electricity based on photo-induced water oxidation at the cathode and enzyme catalyzed oxygen reduction at the cathode under neutral pH conditions. The thylakoids and laccase were molecularly tethered to carbon nanotube modied electrodes using hetero bi-functional cross-linkers. For the rst time in natural photosynthetic systems, multiple membrane proteins have been shown to participate in direct electron transfer with the nanostructured electrode. The origin of photo-activity was conrmed to be from the light induced water-splitting reaction at the oxygen-evolving site of thylakoids. The thylakoid-MWNT composite electrode yielded a maximum current density of 68 mA cm À2 and a steady state current density of 38 mA cm À2 , which are two orders of magnitude larger than those previously reported for similar systems. The direct conversion of light into electricity using plant thylakoids demonstrated in this work offers great potential for green energy harvesting. The high photo-electrochemical activity of thylakoids reported here has potential implications in photofuel production and other articial photosynthesis applications.

Cyanobacteria possess unique and exciting features among photosynthetic microorganisms for energy conversion applications. This study focuses on production of direct electricity using a cyanobacterium called Nostoc sp. (NOS) as a photo-biocatalyst immobilized on carbon nanotubes on the anode of photo-bioelectrochemical cells. By illuminating with light (intensity 76 mW cm(-2)) the NOS immobilized on a carbon nanotube (CNT) modified electrode generated a photocurrent density of 30 mA m(-2) at 0.2 V (vs. Ag/AgCl). The contribution of different photosynthetic pigments in NOS to the light capture was analyzed and chlorophyll-a was found to be the major contributor to light capture followed by phycocyanin. Further investigation using a set of inhibitors revealed that the electrons were redirected predominantly from PSII to the CNT through the plastoquinone pool and quinol oxidase. A rudimentary design photosynthetic electrochemical cell has been constructed using NOS/CNT on the anode and laccase/CNT on the cathode as catalysts. The cell generated a maximum current density of 250 mA m(-2) and a peak power density of 35 mW m(-2) without any mediator. By the addition of 1,4-benzoquinone as a redox mediator, the electricity generation capability was significantly enhanced with a current density of 2300 mA m(-2) and a power density of 100 mW m(-2). The power densities achieved in this work are the highest among 'non-engineered' cyanobacteria based electrochemical systems reported to date.

Multicopper oxidases linked to multiwall carbon nanotubes via the molecular tethering reagent, 1-pyrenebutanoic acid, succinimidyl ester, displayed high bioelectrocatalytic activity for oxygen reduction.